Tumble dryers provided with a cabinet inside which there is installed a tunnel-type rotary drum arranged for rotating with respect to a horizontal or inclined geometric axis are well known in the prior art. The tunnel-type drum is provided with a perforated cylindrical wall and with end openings at opposite axial ends. These end openings of the drum are facing corresponding loading and unloading openings formed in the cabinet, which can be opened and closed by means of respective doors. Thus, the clothing to be dried can be introduced into the drum through a loading door at one end and extracted through an unloading door at the opposite end. The loading and unloading doors remain closed during a drying operation. Hot air circulation means which include a chamber surrounding the cylindrical wall of the drum connected to a suction device are configured for radially introducing hot air into the drum through the perforations located in an area of the cylindrical wall which is on one side, preferably an upper side, of the drum and extracting the hot air from the drum through the perforations located in an area of the cylindrical wall which is on an opposite side, preferably a lower side, of the drum while the drum rotates with the clothing tumbling therein. One drawback is that the passage area of the perforations is relatively small compared with the area of the cylindrical wall and this means that the hot air circulation through the perforations is not very efficient and that a large part of the flow circulates around the drum without penetrating therein.
Patent EP-A-1318226 describes a tumble dryer of the type described above in which the drum has a perforated revolution wall revolving around the geometric axis of rotation and wherein any generatrix of said revolution wall, when it is located at the lowest level of the drum, is inclined with respect to the horizontal, with an end adjacent to the inlet door more elevated than an end adjacent to the outlet door. Oblique blades with respect to any generatrix are fixed on a surface inside the drum and they are oriented such that when the drum rotates in a drying direction, the effect of the inclination of the blades offsets a tendency of the clothing to move by gravity towards the outlet door keeping the clothing inside the drum, and when the drum rotates in an opposite unloading direction, the effect of the inclination of the blades is added to said tendency of the clothing to move by gravity towards the outlet door to carry out an automatic operation for unloading the clothing from the drum.
U.S. Pat. No. 4,593,481 discloses a tunnel-type rotary drum tumble dryer wherein the drum which is arranged for rotating with respect to a generally horizontal geometric axis has a cylindrical wall and end openings at opposite ends. The cylindrical wall of the drum has perforated annular portions located on opposite sides of a non-perforated annular portion, and the dryer includes means for circulating hot air radially into the drum through the perforations of one of the perforated annular portions, then axially along the non-perforated annular portion and through the items to be dried, and then radially out of the drum through the perforations of the other perforated annular portion. One drawback of this construction is that the items to be dried, which, as a result of the rotation of the drum tumble on the areas of the drum which are at a lower level, have the tendency to block the perforations of the wall of the drum in these areas located at a lower level forcing the hot air to enter and exit the drum through the perforations of the areas of the drum which are at a higher level, which makes it difficult for the hot air circulating inside the drum to pass through the clothing to be dried and this reduces dryer efficiency.